BACK-UP (16K ZX81)
by D N Venamore, Burgess Hill, Sussex
from Your Computer (July 1984), page 152

This copier for the 16K ZX-81 will duplicate any program up to 15K long
including those which cannot be SAVEd by the normal routine.

The program is a modified version of the ZX-81 LOAD and SAVE routines and
comprises 128 bytes of machine code and a supporting "no-frills" BASIC
program. It fits into 1K with a little to spare.

The program to be copied is loaded above RAMtop, from where it can be saved
as required.

Before typing in anything,

    POKE 16339,72

and NEW. This sets RAMtop to 18432, which allows sufficient space to enter
and edit the program, but is low enough to collapse the Display File. If
this is not done the expanded Display File will be saved with your
completed program, making it too long to Load into the 1K finally allocated
far it.

It is necessary to reset RAMtop to 17408 and load the program.

I prefer to set RAMtop using the short program. I keep this on tape in
front of the COPY program with approx. 10 sees of tape running between them.

Whichever you prefer, enter New. Set RAMtop using the RAMtop program or

    POKE 16389,68

Now reload COPY and run it.

The first prompt asks for the name of the program to be copied. Note that
the name is not used to find the named program on the tape.

After entering the name and NEWLINE, the next prompt appears, "Start Tape
then NEWLINE".

Audibly monitor the program to be copied and locate the start of the 5
second silent period which precedes the program proper. Stop the tape
there. Then with the recorder set for LOAD, start the tape and press
NEWLINE immediately.

When the program is LOADed, the prompt "LOADed-Start Blank Tape then
NEWLINE to SAVE" appears. Place a clean tape in the recorder set for SAVE,
run tape and press NEWLINE.

When the program has SAVEd, the option to take further copies is presented.
The BREAK key may be used to abort both LOAD and SAVE routines.

After BREAK, RUN will return you to the LOAD routine. GOTO 180 will return
you to the SAVE routine.
